These are plants that float on the surface of the water and are not rooted in the pond bottom. The most common of these are duckweed and filamentous algae. Some plants, such as lotus and some pondweeds, are rooted in the bottom but have leaves that float on the surface. These are not true floating plants, but actually combine the characteristics of submerged plants and floating plants.
Filamentous Algae. (pictured right) Filamentous algae is most often seen as a slimy yellowish green mat on the surface of the pond. This mat is made up of tiny hairlike algae filaments. These filaments grow attached to the bottom of the pond and can often be seen early in the year as green “fuzz,” or “hair” on the bottom. When filamentous algae produce oxygen it is trapped in their filaments. At some point in time, enough oxygen is trapped to make the mat buoyant and the entire mass floats to the surface. The mat then remains there until it is broken apart by heavy wind or rain, or until the algae dies.
Planktonic Algae. (pictured left) This type of algae consists of microscopic plants, usually suspended in the upper few feet of water or floating on the surface. Water appears pea soup green, brown, or may have the appearance of bright green paint spilled in the pond. A sudden die-off may cause summerkill of fish due to oxygen depletion. Some forms of planktonic algae may be toxic to livestock, wildlife, and humans, and it may impart taste or odor to the water. Although uncommon in most ponds, nutrient-rich ponds are especially vulnerable and may become plagued with dense plankton blooms.
Duckweed and Watermeal. Duckweed and the closely related watermeal have the distinction of being the smallest flowering plants in the world. Both plants can cause big problems in ponds. Duckweed generally has one to three oval leaves that seldom measure more than a quarter of an inch in size. These leaves may have one or two hairlike roots hanging down into the water from the underside of the leaf. Watermeal looks like very small green grains floating on the surface of the water. It is often mistaken for seeds. No roots are visible. These plants can be extremely abundant in ponds where they are often are piled up by the wind until several layers high. This makes them extremely difficult to control because it is next to impossible to get good herbicide coverage over all the plants.
Pond Lilies. There are many species of plants that can loosely be called pond lilies. They are all perennials with relatively large leaves that lay flat on the surface of the water, distinguishing them from spatterdock (a lily-like emergent plant). Depending on the species, these leaves can be round or elliptical and may or may not have a slit in one side of the leaf. Like spatterdock, pond lilies have large root systems that send up shoots. In most cases, pond lilies do not become abundant enough to cause problems, however, some species can become quite dense under the right circumstances.
Learn about aquatic vegetation control methods.